The CIA director has warned US President-elect Donald Trump it would be an act of "folly" to scrap the nuclear deal with Iran.
John Brennan told the BBC it would be "disastrous" to end the deal designed to prevent Tehran from developing nuclear weapons.
Mr Trump threatened during the presidential election campaign to scrap the deal, but Mr Brennan said doing so would strengthen hardliners in Iran and possibly spur other countries to pursue nuclear weaponry.
The CIA director also suggested Mr Trump should be wary of promises made by Russia because of the past failure to deliver.
He said Moscow and the Syrian regime are responsible for the horrendous humanitarian situation facing Syrian civilians.
Mr Brennan plans to step down in January.